Zinc is an essential trace element in the diet of all living organisms from bacteria to humans. Either too little zinc or too much zinc can be harmful, causing health problems. The severity of health effects will depend on how much zinc a person has been exposed to, for how long, the nature of the zinc compound(s), and current state of health. A human body (70 kg) contains about two grams of zinc. The recommended dietary allowance (RDA) for zinc is 15 milligrams a day for men, 12 milligrams a day for women, 10 milligrams a day for children and 5 milligrams a day for infants.
Not enough zinc in the diet can result in a loss of appetite, a decreased sense of taste and smell, slow wound healing and skin sores, or a damaged immune system. Young men who don't get enough zinc may have poorly developed sex organs and slow growth. If a pregnant woman doesn't get enough zinc, her babies may have growth retardation. Harmful health effects generally begin at levels in the 100 to 250 milligrams a day range. Eating large amounts of zinc, even for a short time, can cause stomach cramps, nausea, and vomiting. Taken longer, it can cause anaemia, pancreas damage, and lower levels of high density lipoprotein cholesterol (the 'good' form of cholesterol). Ingesting too much zinc may also interfere with the body's ability to absorb and use other essential minerals such as copper and iron. People with potentially high exposure to zinc include those who intentionally consume large doses of zinc as a dietary supplement, and patients who receive chronic treatment with drugs containing zinc salts (such as injectable insulin).
Zinc dust is irritating to the eyes, nose, and throat, and solid zinc compounds are irritating to the skin and eyes. Breathing large amounts of zinc dust can cause a cough with phlegm. Inhaling zinc dust or fumes can cause 'metal fume fever' which affects the lungs and body temperature. Long term effects of breathing high levels of zinc are unknown. Inhalation of zinc oxide fumes is common in occupational exposures and can produce serious injury to the respiratory system. Inhalation of zinc chloride fumes (smoke bombs) can result in coughing, chest pain, and respiratory tract irritation. Other symptoms include blueness of the skin (cyanosis), skin disease (dermatosis), skin inflammation (dermatitis), skin burns, ulceration of nasal passages, deficiency of calcium in the blood (hypocalcaemia), presence of blood traces in the urine (microhematuria), and pneumonitis. The fumes also affect eyes. Death can result from acute high dose inhalation of zinc chloride smoke. Zinc sulfate is astringent and corrosive to skin, and can cause dermatitis, boils, conjunctivitis, gastrointestinal disturbances, vomiting, cramps, renal damage, and inflammation of the pancreas through blood (haemorrhagic pancreatitis). Zinc sulfide is astringent and corrosive to skin, and if ingested with a high gastric acidity may decompose to hydrogen sulfide in the stomach, with subsequent systemic poisoning. In large doses, it can cause vomiting and diarrhoea.
Some zinc compounds are very harmful not because of zinc but because of other harmful constituents that make up the compounds. Examples include:
- zinc chromate (potential carcinogen, with many of the same health effects as chromium and chromates, including ulceration of the nasal septum, chronic rhinitis, respiratory irritations, conjunctivitis, skin ulcers, dizziness, intense thirst, abdominal pain, vomiting, shock, absence of urine (anuria), pharyngitis, dermatitis with fluid effusion (oedema) and ulceration, and death due to retention of urinary constituents (uraemia);
- zinc cyanide (with many of the same health effects as cyanide, including nausea, vomiting, confusion, vertigo, increased intake and depth of respiration (hyperpnoea), breathing difficulties (dyspnoea), headache, dizziness, dermatitis, weak and irregular pulse, blindness, damage to optic nerves and retina, sudden loss of consciousness, convulsions, and death from respiratory arrest);
- zinc fluoride (with many of the same health effects as fluoride, including severe gastritis, abdominal pain, vomiting, diarrhoea, shock, blueness of the skin (cyanosis), weak pulse, low blood pressure, drowsiness, liver injury, hyperactive reflexes, increase in radiographic density of bones (eventually causing anatomical abnormalities), and death from shock); and
- zinc phosphide (may evolve phosphine in the presence of moisture, which can cause intense nausea, abdominal pain, chills, tightness in the chest, breathing difficulties (dyspnoea), cough, shock from toxic heart muscle inflammation (myocarditis), jaundice from liver necrosis, severe gastrointestinal irritation, and fatal pulmonary oedema (fluid in the lungs).
Entering the body
Zinc can be inhaled or ingested.
Zinc (in trace quantities) is essential for human health. Natural zinc levels are present in food and water, and small amounts are regularly ingested. Elevated zinc levels can be encountered when drinking contaminated water near mining and refinery sites, manufacturing or waste sites, or drinking contaminated water or a beverage that has been stored in metal containers or flows through pipes that have been coated with zinc to protect from rust. It may also happen when eating too many dietary supplements that contain zinc. Occupational exposure to higher than normal zinc levels may occur when breathing zinc dust or fumes at various industrial sites (such as smelters, galvanising facilities, etc.).
Australian Drinking Water Guidelines (NHMRC and ARMCANZ, 1996):
Health: Insufficient data to set a guideline value based on health considerations.
Aesthetic: Maximum of 3 mg/L (i.e. 0.003 g/L) before taste problems occur.
Worksafe Australia has defined zinc oxide as hazardous. The exposure standard for zinc oxide dust is 10 milligram/m3 (TWA). For zinc oxide fumes the exposure standard is 5 milligram/m3 (TWA) and 10 milligram/m3 (STEL) respectively. Zinc chloride is an irritant. The exposure standard for zinc chloride fumes is 1 milligram/m3 (TWA) and 2 milligram/m3 (STEL) respectively. Zinc chromate is classified as toxic and its exposure standard is 0.01 milligram/m3 (TWA, as chromium).
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